Background: The usefulness of the mast cell activation test (MAT) in diagnosing patients with uninterpretable basophil activation test (BAT) results caused by nonresponding basophils has not been addressed. Our study evaluated whether the results of the MAT were associated with the severity of the allergic reaction.
Methods: We recruited 39 patients with Hymenoptera venom allergy (HVA), 22 nonsensitized controls, and 37 BAT nonresponding HVA patients. Specific IgE levels for honeybee venom (HBV) and yellow jacket venom (YJV) and total IgE were quantified using the IMMULITE® system. We performed a BAT and a MAT, which was based on the response of LAD2 cells to HBV and YJV.
Results: We first optimized the susceptibility of LAD2 cells to IgE-mediated degranulation in HVA and showed that prestimulation with IL-33 and IL-6 significantly increased the responsiveness of LAD2 cells to allergen stimulation (P<.01). The LAD2 MAT results correlated with the BAT results, and patients with severe sting reactions (Mueller grades III and IV) had a median 2-fold higher LAD2 MAT score than patients with nonsevere sting reactions (large local reaction or Mueller grades I and II) (P<.05). Furthermore, LAD2 MAT provided conclusive results in 20 of the 37 HVA patients (54.1%) with nonresponding basophils in the BAT.
Conclusions: The LAD2 MAT is a new diagnostic tool for HVA patients with nonresponding basophils. LAD2 MAT can identify patients at risk of severe sting reactions and can thus help guide recommendations for venom immunotherapy and improve the management of patients with HVA.

Key words: Basophil activation test nonresponders, Hymenoptera venom allergy, LAD2, Mast cell activation test, Reaction severity